Rotational Speed Sensor Assembly

ABSTRACT

A sensed element is disclosed for incorporation into an apparatus that includes a rotatable shaft. The sensed element includes at least one sensor-detectible feature detectible by a sensing device for use in measuring a rotational speed of the shaft, a base portion coupled to the shaft so as to rotate with the shaft, and a projection extending from the base portion. The projection is engageable with a portion of the apparatus to limit movement of the sensed element along the shaft. The projection may also aid in positioning the sensed element within the apparatus during installation and removal of the sensed element.

BACKGROUND OF THE INVENTION

The present invention relates generally to sensor assemblies formeasuring the rotational speed of an object and, more particularly, toan apparatus for securing a sensed element of a sensor assembly in adesired position along a rotating object to facilitate accuratemeasurement of the rotational speed of the object.

Rotational speed sensor assemblies for measuring the rotational speed ofan object are known in the art. In one application of such systems, arotational speed of a shaft or wheel mounted in a vehicle is measured.In one approach for locating such sensor systems on the vehicle, thesensor system is positioned near the wheel whose speed is to bemeasured. This solution has many disadvantages, including thermalconcerns (temperatures to which the sensor components are exposed mayexceed the rated temperatures of the devices), constraints on thepackaging and mounting of the sensor assembly elements, problems withrouting of signal transmission cables, additional assembly operations,and other concerns.

SUMMARY OF THE INVENTION

The present invention provides a sensed element for incorporation intoan apparatus that includes a rotatable shaft. The sensed elementincludes at least one sensor-detectible feature detectible by a sensingdevice for use in measuring a rotational speed of the shaft, a baseportion coupled to the shaft so as to rotate with the shaft, and aprojection extending from the base portion. The projection is engageablewith a portion of the apparatus to limit movement of the sensed elementalong the shaft. The projection may also aid in positioning the sensedelement within the apparatus during installation and removal of thesensed element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a portion of a differentialassembly containing a rotational speed sensor assembly in accordancewith an embodiment of the present invention.

FIG. 2 is a partial perspective end view of an axle tube in accordancewith an embodiment of the present invention.

FIG. 3 is a view of a lead-in feature formed on splines of a sensedelement in accordance with an embodiment of the present invention.

FIG. 4 is a cross-sectional end view of a sensed element mounted on ashaft in accordance with a particular embodiment of the presentinvention.

FIG. 4A is a cross-sectional end view of a sensed element mounted on ashaft in accordance with another particular embodiment of the presentinvention.

FIG. 4B is a cross-sectional view of a portion of the sensed element ofFIG. 4A.

FIG. 5 is a partial cross-sectional view of a portion of a differentialassembly containing a rotational speed sensor assembly in accordancewith another embodiment of the present invention.

FIG. 5A is a partial cross-sectional view of a portion of the sensedelement shown in FIG. 5.

FIG. 6 is a partial view of a portion of a sensed element including afriction-reducing overmold formed threreon, in accordance with anotherembodiment of the present invention.

FIG. 7 is an isometric view of a sensor-detectible feature incorporatedinto a sensed element in accordance with an embodiment of the presentinvention.

FIG. 8 is a partial plan view of a sensed element showing a detent inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention disclosed herein provide arotational speed sensor assembly including a sensing device mounted inand/or extending into an interior of a differential housing and an axletube containing an axle shaft on which a vehicle wheel is mounted. Thesensor assembly also includes a sensed element rotationally coupled tothe axle shaft and positioned in relation to the sensing device suchthat sensor-detectible features on the sensed element are registered bythe sensing device during rotation of the shaft. While the embodimentsof the sensor assembly mounting system disclosed herein are described asthey may be applied to sensing the rotational speed of a vehicle wheelmounted on an axle shaft, the mounting system disclosed herein couldalso be used for other applications requiring measurement of therotational speed of a body. In addition, it is understood that anembodiment of the rotational speed sensor assembly described herein maybe mounted on any other axle of the vehicle, thereby enabling therotational speed of the other axle(s) to be measured independently.

FIG. 1 shows a rotational speed sensor assembly 10 mounted along an axleshaft 13 and inside a housing 12 of a vehicle differential mechanism(only partially shown). The speed sensor 10 is positioned remotely of avehicle wheel (not shown) which would be to the left as viewed. Housing12 includes a passage 14 formed for mounting of a sensing device 16(described below) therein. The elements of the embodiments of therotational speed sensor assembly 10 described herein may be accessed andserviced by removing a portion of differential housing 12 and/or shaft13. A suitable roller bearing 18 is mounted in differential housing 12for supporting axle shaft 13 and an associated ring gear carrierassembly 41 in a manner known in the art, so as to enable rotation ofthe shaft and the vehicle wheel attached thereto.

An axle tube 20 is secured to and extends through at least a portion ofdifferential housing 12 for mounting of axle shaft 13 therein. In theembodiment shown in FIG. 1, an opening 20 a is formed in a wall of theaxle tube 20. Opening 20 a is aligned with passage 14 in differentialhousing 12 and is configured for mounting of sensing device 16 therein.As seen in FIG. 2, axle tube opening 20 a may extend a predeterminedangular distance Ø along the axle tube wall to provide a degree offlexibility in aligning opening 20 a with passage 14 formed indifferential housing 12 during assembly of the axle tube into thedifferential housing. Similarly, passage 14 formed in differentialhousing 12 may also extend a corresponding angular distance along thedifferential housing to provide a degree of flexibility in positioningof sensing device 16 along the differential housing.

In the embodiments shown herein, axle tube 20 is secured withindifferential housing 12 so as to provide a gap 22 between the axle tubeand bearing 18. As described in greater detail below, a portion of asensed element 26 extends into gap 22 for purposes of locating andretaining the sensed element along a longitudinal axis of shaft 13.

Referring to FIGS. 1 and 4, axle shaft 13 has a series ofaxially-extending splines 13 a formed along an exterior surface thereof.Splines 13 a engage complementary splines or teeth 18 a formed along aninner diameter of ring gear carrier assembly 41, thereby coupling shaft13 to the bearing. However, other methods of rotationally coupling theshaft to the inner bearing ring may also be used.

In the embodiment shown, splines 13 a are also extended along shaft 13to engage complementary splines or teeth 26 b formed along an interioropening 26 e of an annular base portion 26 a of sensed element 26(described in greater detail below), thereby rotationally coupling thesensed element 26 to the shaft 13. In other embodiments (not shown), aseparate series of splines (or one or more other engagement features)are formed along the portion of the shaft 13 to be rotationally coupledto the sensed element 26. These features on the shaft then engagecomplementary features formed along base portion 26 a of sensed element26, to rotationally couple the sensed element to the shaft.

Referring again to FIG. 1, rotational speed sensor assembly 10 includessensed element 26 rotationally coupled to an axle shaft 13 of a vehicle,and a sensing device 16 configured to sense rotation of the sensedelement 26 and to generate an electrical signal corresponding to therotational speed of the sensed device, in a manner known in the art.Embodiments of the sensor assemblies described herein may be employedfor measuring vehicle wheel speeds in anti-lock brake systems ortraction control systems, for example.

The operation of various types of passive and active sensing devices andassociated sensed elements for detection of shaft rotational speeds iswell known. In a typical wheel speed sensor assembly as employed in theembodiments of the present invention, rotation of the sensed element 26in proximity to the sensing device 16 will induce an electromagneticpotential having pulses or a frequency proportional to the relativerotational speed of the sensed element.

Referring again to FIG. 1, the sensing device 16 extends through passage14 formed in the differential housing 12 where an appropriate retainingmeans (not shown) and sealing means (not shown) maintains thepositioning of the sensing device through operation and ensures that oilwithin the housing 18 will not be lost. As seen in FIG. 1, the sensingdevice 16 occupies a position radially spaced apart from the surface ofthe sensed element 26. During installation of the rotational speedsensor assembly 10 into a vehicle, the general tolerances normallymaintained will result in a predetermined distance or air gap betweenthe sensing device 16 and the sensed element 26 which is within desiredoperating limits to insure accurate speed indication. However, thesensing device 16 may be mounted in the differential housing 12 so as topermit adjustment of the air gap between the sensing device and thesensed element to accommodate different types of sensing devices,different types of sensed elements, different diameters and parttolerances of the portion of the sensed element residing opposite thesensing device, and other factors relevant to a particular application.

Any suitable type of sensing device may be used, depending on therequirements of a particular application. Hall Effect sensors,magnetoresistive sensors, and variable reluctance (VR) sensors areexamples of suitable types of sensors for the application describedherein. Sensing device 16 may be operatively coupled to any additionalhardware of software elements (for example, a signal translation module,CPU, controller, or other element(s)) required for processing of thesensed signals, as is known in the art.

Referring again to FIG. 1, and as previously described, a plurality ofaxially-extending splines 26 b is formed along an interior surface ofannular base portion 26 a. Splines 26 b are configured to engagecomplementary splines 13 a formed along the exterior of shaft 13,thereby rotationally coupling the sensed element 26 to the shaft 13.Splines 26 b may be dimensioned so as to slidingly engage shaft splines13 a during insertion of shaft 13 into the central opening 26 e in baseportion 26 a. Interior splines 26 b may be formed from any suitablematerial, such as a metallic or polymer material.

Shaft splines 13 a and complementary base portion splines 26 b may haveany desired spacing or arrangement along the respective surfaces fromwhich they project. In one embodiment, shaft splines 13 a and baseportions splines 26 b are evenly spaced apart. Referring to FIG. 4, in aparticular embodiment, four angularly spaced-apart base portion splines26 b are provided for engaging correspondingly spaced-apart grooves 13 bformed between adjacent pairs of spaced-apart shaft splines 13 a.Alternatively, a lesser number or a greater number of base portionsplines 26 b may be provided to engage a corresponding number of groovesformed in shaft 13. Also, in the embodiment shown in FIG. 4, a surface26 j defined by an inner diameter of annular base portion 26 a (and fromwhich base portion splines 26 b extend radially inwardly) circumscribesthe outermost surfaces of shaft splines 13 a. Because every groove 13 bbetween adjacent shaft splines 13 a is not occupied by a correspondingbase portion spline 26 b, a pathway for oil or lubricant flow isprovided along the shaft 13 via each of the unoccupied grooves 13 b.These pathways are useful ways to provide lubrication to the outer axleshaft bearings (not shown) with lubricant traveling from thedifferential.

Referring to FIG. 3, in a particular embodiment, each of splines 26 b ofsensed element 26 includes a chamfer or lead-in 26 g for facilitatinginsertion of axle shaft 13 into sensed element 26. Each of base portionsplines 26 b includes a narrowed or tapered lead-in portion 26 m to aidin locating and centering the base portion spline 26 b betweenrespective adjacent ones of shaft splines 13 a during insertion of theshaft 13 into the sensed element base portion opening 26 e.

Referring to FIGS. 1, 5, 5A, and 7, sensed element base portion 26 aincludes sensor-detectible features forming a target wheel or tone ring.These sensor-detectible features enable measurement of the rotationalspeed of the base portion by one of the sensing devices previouslydescribed when the base portion 26 a is coupled to shaft 13. Thematerials used to form the sensor-detectible features of the baseportion 26 a and the structures of the sensor-detectible features areaffected by the type of sensing device to be used. Numerous examples ofsuch sensor-detectible features are known in the art.

In one example (shown in FIGS. 5 and 5A), the base portion 26 a′ ofsensed element 26′ includes a series of alternating, axially-extendinglands 26 c′ and grooves 26 d′ formed along an exterior of the baseportion. The lands 26 c′ and grooves 26 d′ are formed from steel oranother ferromagnetic material. In a particular application, metallicportions of the sensed element 26′ are formed from a ferromagneticpowdered metal, which is die-formed and then sintered into the desiredfinished form.

Alternatively, the entire sensed element 26 or the base portion 26 aalone may be formed from a polymeric or elastomeric material, withferromagnetic, magnetic, or ferrous elements embedded therein orotherwise secured thereto so as to be detectable by the sensing device.Sensor-detectible elements may be affixed to an outer surface of thebase portion, using adhesive bonding or other suitable means. Otherpossible combinations of structures and materials are also suitable forconstructing a sensed element suitable for the purposes describedherein. For example, elements comprising alternating pairs of north andsouth magnetic poles may be molded into the polymeric or elastomericmaterial, or the alternating pairs of poles may be affixed to anexterior of the base portion by use of a suitable adhesive, for example.

In another example (shown in FIG. 1), the sensor-detectible features areprovided by an annular metallic ring 26F embedded in or molded into apolymeric base portion material. An example of a metallic ring suitablefor use in such an embodiment is shown in FIG. 7 Referring again to FIG.1, the extent 26h along base portion 26 a of the sensor-detectiblefeatures and the positioning of these features along the base portionare specified so as to ensure that the features will be detectible alongthe entire range of movement of the sensed element along shaft 13 whenthe shaft and sensed element are rotating. This helps to avoid loss ofsensor signals due to misalignment between the sensor and thesensor-detectible features.

The embodiments of the sensed element described herein are also providedwith one or more axial positioning features for locating and securingthe sensed element along shaft 13. These axial positioning features areengageable with another portion of the vehicle to limit movement ofsensed element 26 along the shaft 13 during rotation of the shaft.

Referring to FIG. 1, in one particular embodiment, a flange 30 extendsradially away from base portion 26 a and into gap 22 between axle tube20 and bearing 18. In the embodiment shown, the flange extends in acontinuous 360° arc around the base portion. In other embodiments (notshown), the flange does not extend in a continuous fashion around thebase portion, but rather has a multi-lobed configuration. Depending onthe material(s) from which the flange is formed, this configuration mayreduce the weight of the flange, the amount of material used tofabricate the flange, and the energy required to rotate the sensedelement. Depending on the requirements of a particular application andmanufacturing preferences, flange 30 may be formed integral with baseportion 26 a or the flange may be formed as a separate part and attachedto the base portion using any suitable means. Flange 30 may be formedfrom any suitable material, such as a metallic or polymer material.

In another embodiment (shown in FIG. 5), flange 30 is dimensioned andpositioned inside axle tube 20 such that a portion of the flange residesin the gap 22 prior to insertion of shaft 13 into the axle tube. It isseen that, once shaft 13 has been positioned inside the axle tube 20,movement of sensed element 26 along shaft 13 will be constrained byabutting contact between the flange 30 and the edge of the axle tube ifthe sensed element moves along shaft 13 in the direction indicated byarrow “A”. Similarly, movement of sensed element 26 along shaft 13 willbe constrained by abutting contact and between the flange 30 and thebearing 18 if the sensed element moves along shaft 13 in the directionindicated by arrow “B”. Thus, the flange 30 initially acts to axiallyposition and secure the sensed element along shaft 13 during rotation ofthe shaft. The flange 30 may also be used to temporarily position thesensed element 26 within axle tube 20 until the axle shaft 13 isinserted into the sensed element 26.

If desired, the flange 30 or a portion of the flange may be coated witha low-friction coating (not shown) to aid in minimizing any contactfriction between the flange and axle tube 20, and between the flange andbearing 18. Alternatively, as seen in FIG. 6, the portion of the flangeresiding in gap 22 may be overmolded with a relatively low-frictionmaterial 33, such as Delrin® or an acetal polymer, for example.Referring to FIG. 1, in another embodiment, a shim 32 is providedadjacent to a portion of bearing 18 subject to contact with flange 30,to aid in minimizing any contact friction between the flange and thebearing and to aid in removing differential end play between the flangeand bearing 18. A similar shin (not shown) may be attached to theportion of axle tube (or to a portion of any other element) subjected tocontact with the flange.

Referring to FIG. 4, holes 38 may be formed in flange 30 to enable oilto pass through the flange, to aid in lubrication of the wheel bearing.In a particular embodiment (shown in FIGS. 4A and 4B), each hole of atleast a portion of holes 38″ extends through the flange 30 parallel toan axis A″ formed at an angle α with respect to a line passing throughthe center of the hole and which extends substantially parallel with anaxis X about which flange 30″ (and also shaft 13) rotates. When flange30″ is immersed in lubricating oil and rotated, oil is forced throughthe angular holes 38″ to aid in lubricating the outer bearings. Thus,the rotating flange with angular holes 38″ acts as a fluid pump.

In another alternative embodiment (not shown), the flange 30 extendsinto a groove or other feature formed into axle tube 20 or anotherelement of the vehicle. This groove confines the extending portion offlange 30 to correspondingly restrict movement of the sensed elementalong shaft 13. That is, movement of the sensed element along the shaftafter the sensed element has been properly positioned along the shaftwill cause the flange to abut a wall of the groove, thereby preventingfurther motion of the flange within the groove and also preventingfurther motion of the sensed element along the shaft.

Referring to FIGS. 1 and 8, in another embodiment of a sensed elementaxial positioning feature, a cantilevered detent 36 extends from baseportion 26 a to engage the shaft 13 along a depression or cavity 40formed in the shaft when the shaft is properly positioned relative tothe sensed element 26, which has been previously positioned within theaxle tube 20. As shown in FIG. 1, depression 40 may extend 360° aroundthe outer surface of the shaft in order to simplify location of thedetent within the depression during installation. Detent 36 isconfigured so as to resiliently deflect due to contact with the shaft 13while the shaft is being inserted into the base portion central opening26 e. The detent then snaps or slides into cavity 40 when the desiredpositional relationship between the shaft 13 and the sensed element 26has been achieved (i.e., when shaft splines 13 a are engaged with baseportion splines 26 b and the sensor-detectible features located alongbase portion 26 a are properly aligned with sensing device 16). Detent36 may also be dimensioned such that it will be too large to fit withinany of the grooves between the shaft splines, thereby preventing thedetent from entering the grooves during installation of the sensedelement 26 or installation of shaft 13.

In addition, it is seen that after the sensed element 26 has beenproperly positioned along the shaft, motion of the sensed element alongshaft 13 in either of directions “A” or “B” will produce a progressivedeflection of the detent as the detent moves closer to an edge of thedepression 40. As used herein, the term “progressive” is understood tomean continuously increasing in extent or severity. This progressivedeflection results in an increased contact force between the detent andthe shaft which acts to resist further motion of the sensed element inthe direction of movement, because continued movement of the sensedelement along the shaft will cause an increasing deflection of thedetent, resulting in a greater reaction force which is manifested as thecontact force between the detent and the shaft. By this mechanism, thedesired position of the sensed element along the shaft is substantiallymaintained.

The depression 40 and the detent 36 may be dimensioned such thatsufficient contact force is generated by axial displacement of thesensed element from its desired position to maintain the sensed elementwithin a relatively narrow range centered about a desired position ofthe sensed element along the shaft. Also, detent 36 may be formedintegrally with base portion 26 a as shown in FIG. 8, or the detent maybe formed as a separate part and secured to the base portion 26 a usingany suitable method. Detent 36 may be formed from any suitable material,for example, a metallic or polymer material. In a particular embodiment(shown in FIG. 1), detent 36 is used in conjunction with flange 30 toposition and retain sensed element 26 along shaft 13.

In other alternative embodiments (not shown), a snap ring or otherconventional hardware element may be affixed in a suitable groove formedon the shaft or in any other suitable feature for securing the sensedelement in position axially along shaft 13.

The entire sensed element 26 (including base portion 26 a and anyprojections extending therefrom as described above) may be formed as asingle piece from a polymer material, a metallic material, or any othersuitable material.

It will be understood that the foregoing description of an embodiment ofthe present invention is for illustrative purposes only. As such, thevarious structural and operational features herein disclosed aresusceptible to a number of modifications commensurate with the abilitiesof one of ordinary skill in the art, none of which departs from thescope of the present invention as defined in the appended claims.

1. A sensed element for incorporation into an apparatus including arotatable shaft, the element comprising: a base portion mountable on theshaft so as to rotate with the shaft; at least one sensor-detectiblefeature coupled to the base portion for use in measuring a rotationalspeed of the shaft; and a projection extending from the base portion andengageable with a portion of the apparatus to limit movement of thesensed element along the shaft.
 2. The sensed element of claim 1 whereinthe projection comprises a flange projecting substantially radially awayfrom the base portion.
 3. The sensed element of claim 2 wherein theflange extends in a 360° arc around the base portion.
 4. The sensedelement of claim 2 wherein a plurality of openings are formed in theflange to permit passage of a lubricant therethrough.
 5. The sensedelement of claim 4 wherein the flange has an axis of rotation, andwherein each opening of at least a portion of the openings of theplurality of openings extends through the flange parallel to an axisformed at an angle α with respect to a line which passes through acenter of the opening and which is substantially parallel with theflange axis of rotation.
 6. The sensed element of claim 1 wherein theprojection comprises a detent for engaging the shaft to limit movementof the sensed element along the shaft.
 7. An apparatus comprising: arotatable shaft; and a sensed element in accordance with claim 1 mountedon the shaft.
 8. The apparatus of claim 7 wherein the apparatuscomprises a vehicle.
 9. The apparatus of claim 7 wherein the projectionextends into a gap between adjacent elements of the apparatus, andwherein a motion of the sensed element along the shaft in a firstdirection brings the projection into contact with one of the adjacentelements of the apparatus, thereby preventing further movement of thesensed element along the shaft in the first direction.
 10. The apparatusof claim 9 wherein a quantity of a relatively low-friction material ispositioned at a contact interface between the projection and the one ofthe adjacent elements of the apparatus, for reducing contact frictionbetween the projection and the one of the adjacent elements of theapparatus.
 11. The apparatus of claim 10 wherein the adjacent elementsof the apparatus include an axle tube enclosing the shaft and a bearingsupporting the shaft.
 12. The apparatus of claim 7 wherein the shaft hasa depression formed therealong and wherein the projection comprises adetent which engages the shaft along a portion of the depression tolimit movement of the sensed element along the shaft.
 13. The apparatusof claim 12 wherein movement of the sensed element in a first directionwhen the detent is engaged with the depression produces a progressivedeflection of the detent, and wherein the progressive deflection of thedetent produces a force resisting further motion of the sensed elementin the first direction.
 14. The apparatus of claim 12 wherein the detentextends from the base portion in a direction substantially parallel toan axis of the shaft.
 15. The apparatus of claim 7 wherein the shaft hasa plurality of splines formed thereon, wherein the base portion has aplurality of splines projecting into a central opening thereof, andwherein the base portion splines complementarily engage at least aportion of the splines of the plurality of the shaft splines torotationally couple the sensed element to the shaft.
 16. The sensedelement of claim 15 wherein the number of base portion splines is atleast three.
 17. A sensor assembly for detecting a speed of a vehicleaxle shaft, the sensor assembly including a sensed element in accordancewith claim 1 mountable to the axle shaft.